The present invention relates to a controller for electric vehicles driven by motors with an inverter using vector control, particularly, a controller for electric vehicles performing torque control for re-adhering by detecting slipping or skidding generated between wheels and rails.
As a prior art, a method for controlling re-adhesion by detecting slipping or skidding of wheel of electric vehicles, and reducing generated torque of motors has been disclosed in JP-A-4-197004 (1992). A method for detecting re-adhesion of wheel was disclosed in JPA-4-69003 (1992). A technique for driving motors of electric vehicles of railway by vector control of inverters was disclosed in JP-A-5-83976 (1993).
In accordance with the conventional re-adhesion controlling method disclosed in the above JP-A-4-197004 (1992), the slipping of wheel is detected by a method which recognizes whether a changing rate with time (differential value) of the rotor frequency (proportional to the wheel velocity) of the induction motor exceeds a fixed detecting level or not, and a control to reduce the motor torque is performed only during a period when the slipping is detected. However, if the differential value becomes smaller than a designated value, the recognition of the slipping is canceled, and the motor torque is controlled to resume irrelevant to whether the wheel are practically re-adhered or not. Therefore, if the wheel is not re-adhered practically, slipping the wheel occurs instantaneously, and a problem occurs that the slipping phenomena are generated very often repeatedly.
A method for controlling the torque by detecting the re-adhesion is disclosed in the above JP-A-4-69003 (1992), and the method for detecting the re-adhesion is explained hereinafter referring to FIG. 10. The re-adhesion is detected by recognizing that a twice differential value fr" (an axis jerking value) of the rotor frequency fr (proportional to the wheel velocity) at the time t2 exceeds a designated value Le, after detecting the slipping at the time t1.
However, the following problem can be anticipated with the detection of slipping using the twice differential value fr". First, if the wheel velocity behaves as shown in FIG. 11 when re-adhering, the twice differential value fr" of the wheel velocity does not exceed the designated value Le, and the re-adhesion can not be detected nevertheless the re-adhesion occurred at the time t2. Consequently, the torque is maintained in a reduced condition continuously, and a problem that the reduced acceleration of the electric vehicle is generated. Furthermore, in a case if the slipping, which has been likely to converge on an end, is re-generated at the time t1a as shown in FIG. 12, the twice differential value fr" exceeds the designated value Le at the time t1a, and a problem that the re-adhesion is erroneously detected and the slipping is continued is generated.
These kind of problems can be caused when the skidding is generated. As explained above, the conventional technology has a problem that the re-adhesion can not be detected, or the re-adhesion is detected erroneously depending on conditions of slipping or skidding.
Currently, an inverter with vector control such as disclosed in JP-A-5-83976 (1993) come to be used as a controller of induction motors for driving electric vehicles. However, any technology to utilize performance of the vector control for controlling the re-adhesion has not been disclosed.